The shank of a monkey wrench has a "notch" to help support the "back strain" of the adjusting screw against a two-part ferrule and handle.

The notch in the shank supports the ferrule, and is distinct from the "jog bar" which stiffens the shank adjacent to the fixed jaw and head. A.G. Coes & Co. was advertising this feature as the "Patent Lock Ferrule" in the early 1870s along with the "jog bar" based on A.C. Richards' Feb. 7, 1860 patent no. 27,090, and movable jaw improvements from Aury Coes' May 2, 1871 patent 114,505.